Hydraulically expansible drill bits



Aug. 14, 1956 A. w. KAMMERER, JR 2,758,819

HYDRAULICALLY EXPANSIBLE DRILL BITS Filed Aug. 25, 1954 INVENTOR. AECHEE 5V: RAM/WEBER, tie.

United States Patent HYDRAULICALLY EXPANSIBLE DRILL BITS Archer W. Kammerer, Jr., Fullerton, Califi, assignor, by direct and mesne assignments, to Rotary Oil Tool Company, Huntington Park, Califl, a corporation of California Application August 25, 1954, Serial No. 452,181

20 Claims. (Cl. 255-76) The present invention relates to rotary drill bits of the expansible type capable of drilling or enlarging bore holes below a string of well casing to a greater diameter than the inside diameter of the casing string through which the bits are capable of moving.

An object of the present invention is to provide improved rotary drill bits embodying one or more cutters that are expanded outwardly by the hydraulic pressure of the fluid in the drill string to which the bit is attached.

Another object of the invention is to provide a rotary expansion drill bit containing .a mandrel telescope in the body of the bit, in which the cutters are expanded laterally outward by hydraulic forces acting upon the bit body to shift it with respect to the mandrel.

A further object of the invention is to provide a rotary expansible drill bit embodying a mandrel telescoped in the body, in which the cutters are first expanded laterally outward by hydraulic forces acting upon the body to shift it with respect to the mandrel, whereupon the cutters are positively locked in their outwardly expanded position.

Yet another object of the invention is to provide a rotary expansible drill bit, in which the cutters are hydraulically expanded outwardly, and in which drilling weight imposed upon the bit can be utilized to complete the outward expansion of the cutters in the event that full hydraulic expansion does not occur.

Still a further object of the invention is to provide a rotary expansible drill bit of comparatively simple and sturdy construction, relatively short in length, and economical to manufacture.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a longitudinal section through an embodiment of the invention disposed in a well bore, with the cutters and other parts in their initial and retracted positions;

Fig. 2 is a longitudinal section similar to Fig. 1, disclosing the cutters locked in their fully expanded position.

As shown in the drawings, a rotary expansible drill bit A is secured to the lower end of a string of drill pipe B that extends to the top of the well bore C and by means of which the drill bit is lowered through a string of well casing D to a region therebelow where the hole enlarging operation is to commence. The general type of expansible drill bit disclosed in the drawings is shown and described in Patent No. 2,545,036, to which attention is invited for certain structural details.

The upper portion of the rotary drill bit consists of a mandrel having an upper pin 11 threadedly connected 2,758,819 Patented Aug. 14, 1956 to a sub 12 forming the lower end of the string of drill pipe B. This mandrel includes an upper Kelly or drill stem member 13 slidably splined to the man body 14 of the drill bit. The exterior 13 of the lower portion of the kelly is non-circular in shape, being telescopically .received in a companion non-circular socket 16 formed in the main bit body. Specifically, the Kelly exterior 15 and the socket 16 may be of hexagonal shape, to enable the kelly to be moved longitudinally with respect to the body, while still being capable of transmitting rotary movement to the body 14.

The mandrel 10 has a limited range of longitudinal movement within the body 14, its downward movement being determined by engagement of the lower end 17 of the kelly with an inwardly directed body shoulder 18 and its upward movement being limited by engagement of an external shoulder or piston portion 19 of the kelly with one or more stop rings 20 that may be split, to enable them to be inserted within an internal groove 21 in the main body of the bit, the stop rings extending into a cylinder space 22 formed between the Kelly or drill stem 13 and the body 14 of the tool.

The body 14 has a plurality of expansible parts mounted on it. These include cutter supporting members 23 pivotally mounted in body slots '24 on hinge pins 25 suitably secured to the body, to prevent their loss therefrom. Each cutter supporting member 23 depends from the hinge pin 25 and terminates in a bearing supporting pin 26 inclined inwardly and downwardly. A side roller cutter 27 is rotatably mounted on each bearing supporting pin 26, being mounted upon anti-friction roller and ball bearing elements, 2%, 29 rollable on the bearing supporting pin. The ball bearing elements 29 serve to lock the cutter 27 against endwise movement on the bearing supporting pin 26, as well as to transmit axial and radial thrusts, the roller bearing elements 28 transmitting primarily radial thrusts. The manner of mounting the ball and roller bearing elements 29, 28 between the cutter 27 and bearing supporting pin 26 is specifically described in the above-mentioned Patent No. 2,545,036.

The cutter supporting members 23 and the cutters 27 themselves tend to occupy a retracted position substantially entirely within the confines of the main body 14 of the bit. These cutter supporting members and the cutters are expandible outwardly, to enlarge the sides of the wall bore C and to operate upon a formation shoulder E that the cutters form in the latter. To accomplish the expansion, each cutter supporting member 23 has an inclined expander surface 30 on its inner portion 31 below the hinge pin 25 which tapers in a downward and inward direction. Each expander surface 39 terminates in a lock surface 32 formed on a lock portion 33 of the cutter supporting member. The outward expansion is accomplished by producing relative longitudinal movement between the mandrel 10 and the bit body 14, which will produce relative longitudinal movement between the cutter supporting members 23 and the tubular member 34 of the mandrel. This tubular member 34 includes a lower portion 35 slidable within a guide 35 secured to the body 14 and extending across the body slots 24. This guide is disposed below the lock portions 33 of the cutter supporting members.

Located initially substantially above the guide 36 and below the hinge pins 25 and in cutter member recesses 37 is a mandrel lock and expander 38 which has outer surfaces 39 adapted to engage the expander surfaces 30 and the lock surfaces 32. The lock and expander 38 may be formed integral with the tubular member 34, the upper end of the latter being piloted within a socket 40 formed in the lower portion of the kelly 13. An enlarged boss 41 on the tubular member engages a downwardly facing shoulder 42 of the kelly, the tubular member being held against this shoulder by a suitable split retainer or lock ring 43 snapped into an internal groove 44 encompassing the Kelly socket 40 and engaging a downwardly directed shoulder 45 formed on the tubular member boss 41.

In order to facilitate passage of drilling or other fluid down through the central passage 46 in the Kelly or drill stem 13 and into the central passage 47 extending com pletely through the tubular member 34, the latter has a portion 48 extending upwardly from its boss 41 and provided with an upwardly flaring end 49 merging smoothly into the lower surface 50 of the Kelly passage 46. Leakage of fluid around the exterior of the tubular member 34 is prevented by providing a suitable side seal ring 51 such as a rubber ring, in a peripheral groove 52 in the boss 41, which engages the wall of the Kelly socket 40.

Assuming that the body 14 of the tool is elevated relatively along the tubular mandrel 10, the inclined expander surfaces 30 of the cutter supporting members 23 will be shifted upwardly along the lock and expander portion 38 of the tubular member. During such upward shifting, the cutter supporting members 23, and the cutters 27 carried thereby will be pivoted about the hinge pins and urged in an outward direction. The upward movement of the body 14 with respect to the tubular mandrel 10 can continue until the cutters 27 have been shifted outwardly to their fullest extent, as determined by engagement of stop shoulders 53 on the cutter supporting members with companion shoulders 54 formed in the body on opposite sides of the body slots 24. When such engagement occurs, the lower end 17 of the Kelly portion of the tubular mandrel 10 will engage the body shoulder 18, and the lock and expander 38 on the tubular member 34 will be disposed behind and in engagement with the lock portions 33 on the cutter supporting members 23.

It is to be noted that the surfaces 32 of the lock portions of the cutter supporting members 23 and the companion surfaces 39 on the lock and expander portion 38 of the tubular member are substantially parallel to the axis of the drill bit, to prevent the reactive forces of the formation on the cutters 27 from moving the latter inwardly. As a practical matter, it is preferred that the coengaging lock surfaces 32, 39 be inclined slightly in a downward direction toward the axis of the tool, to insure release of the lock and the expander portion 38 from the cutter supporting members 23 when the latter and the cutters 27 are to be shifted to a retracted position.

The relative longitudinal movement between the tubular mandrel 10 and the body 14 of the tool is accomplished hydraulically, in the specific form of apparatus disclosed in the drawings. Thus, the piston or enlarged portion 19 on the drill stem 13 is received within a counterbore 60 formed on the upper portion 14a of the body 14 of the tool. This upper portion 14a actually constitutes a cylinder having a cylindrical wall 61 extending from a lower shoulder 62, defining the bottom of the counterbore, to an upper head and guide 63 which has a depending portion 64 inserted in the upper end of the cylinder and releasably retained therein by a split snap ring 65 carried in a groove in the cylinder head portion 64 and adapted to be received within a generally l-shaped internal groove 66 in the upper portion of the cylinder wall. The head 63 with the snap ring 65 therein, need merely be forced into the cylinder 14a, and, when located opposite the V-shaped groove 66 the snap ring will expand inherently partially into the latter, to releasably lock the cylinder head 63 to the cylinder 14a.

The confined cylinder space 22 is formed between the piston portion 19 of the kelly 13, the periphery of the kelly above the piston, and the cylinder 14a. Thus, a suitable packing or side seal structure 67 may be disposed in a suitable piston ring groove 68 formed in the piston, which is adapted to slidably seal against the cylindrical wall 61 of the cylinder 14a. Fluid is thereby prevented from passing in a downward direction between the piston 19 and the cylinder 14a. Similarly, fluid is prevented from passing in an upward direction out of the annular cylinder space 22 by a cylinder packing or sealing structure 69 secured to the cylinder 14a and slidably engaging the periphery of the kelly 13. This structure may take any suitable form. As disclosed, it consists of a lower packing supporting ring 70 resting upon a split retainer ring 71 received within an internal groove 72 in the cylinder 14a. A non-metallic packing 23, which may be made of any suitable material, rests upon the ring 20, with its upper end engaging an upper backing ring 74 bearing against a split retainer ring 75 received within an internal groove 76 in the cylinder 14a. It is evident that the upper and lower split retainer rings 75, 71 prevent longitudinal movement of the packing structure with respect to the bit body cylinder 14a, the non-metallic packing portion '73 of the sealing structure 69 engaging the cylinder wall 61 to prevent leakage therealong and also slidably engaging the periphery of the drill stem portion 13 of the tubular mandrel 10.

Fluid under pressure in the string of drill pipe B and in the tubular mandrel 10 can be fed into the cylinder space 22 through one or more side ports 77 establishing communication between the central passage 45 through the kelly 13 and the cylinder space. Such fluid under pressure is developed, in the form of invention disclosed in the drawings, by virtue of the fact that the passage 47 through the tubular member 34 of the mandrel is of a restricted diameter, as compared to the passage 46 through the Kelly portion 13 of the mandrel. As a result, the pumping of drilling mud, or other fluid, at an adequate rate through the apparatus will build up a back pressure of fluid in the passage 46, which pressure will be imposed on the fluid in the cylinder space 22, acting upon the packing structure 69 to urge the body 14 of the tool in an upward direction with respect to the tubular mandrel 10, to secure the outward expansion of the cutter supporting member 23 and cutters 27 to their fullest extent.

The rotary expansible drill bit A is run in the well casing D, with the cutter supporting members 23 and the cutters 27 in their initial retracted position. The wall of the well casing will prevent the outward expansion of the cutters, the supporting members merely sliding along the wall of the casing during descent of the apparatus. When the apparatus has been lowered below the casing shoe F, the pumps at the top of the well bore are started to pump fluid at a suflicient rate through the drill pipe B and the tubular mandrel passages 46, 47. Pumping of the fluid builds up a back pressure in the Kelly passage 46, and in the fluid in the ports 77 and cylinder space 22, which pressure will act upon the cylinder packing structure 69 to urge the body 14, the cutter supporting members 23 and cutters 27 in an upward direction with respect to the mandrel 10.

During such upward movement, the expander surfaces 30 of the cutter supporting members 23 are brought to bear against the lock and expander portion 38 of the mandrel, the cutters 27 being urged in an outward direction against the wall of the well bore C. The drill pipe B and the rotary drill bit A are rotated at the proper speed while fluid is being pumped through the apparatus, the cutters 27 enlarging the well bore without the drill pipe being moved vertically. As the cutters enlarge the well bore, the hydraulic force acting upon the body 14 raises the body, the cutter supporting members 23 and the cutters 27 to a further extent, to further expand the cutters outwardly, until the maximum expansion of the cutters has occurred, as determined by engagement of the supporting member stop shoulders 53 with the companion body stop shoulders 54, and the engagement of the body shoulder 18 with the lower end 17 of the Kelly portion 13 of the tubular mandrel 10. As was explained above, with the parts in this position the lock portions 33 of the cutter supporting members 23 will bear against the lock and expander portion 38 of the tubular member 34, to preclude inadvertent partial retraction of the cutters 27 from their fully expanded position.

Downweight of the proper amount can now be imposed on the string of drill pipe B, this downweight being transmitted through the kelly 13 to the body shoulder 18 and from the body through the stop shoulders 54 directly to the cutter supporting members 23 and the cutters 2'7, urging the teeth of the latter into the transverse formation shoulder E previously produced, in order to drill away the formation shoulder and enlarge the well bore to the required diameter and along the desired length of hole. Inasmuch as the downweight is being imposed upon the cutters 27, it is immaterial whether hydraulic pressure within the tool is maintained, since the downward telescoping of the mandrel within the body 14 will retain the cutters in their outwardly locked position. In other words, it is only necessary for the hydraulic portion of the apparatus to be effective during the outward expansion of the cutter supporting members 23 to their fullest extent.

In the event it is desired to retrieve the apparatus A from the well bore after the hole enlarging operation has been completed, or as a result of the cutters 27 becoming worn, it is only necessary to discontinue the pumping of the drilling fluid through the drill pipe B and the apparatus, to relieve the pressure in the cylinder 14a, and to elevate the drill pipe. Such elevating movement will elevate the tubular mandrel lit with respect to the body 14 and the cutter supporting members 23, to raise the lock and expander portion 38 above the expander surfaces 30, whereupon the cutters 27 can drop back to their retracted position. In the event the cutters are reluctant to move to their retracted position, the outer surfaces of the cutter supporting members 23 will engage the casing shoe P, which will then force them inwardly, whereupon the apparatus can be withdrawn through the well casing P to the top of the hole.

If, for some reason, the cutters 27 are not expanded outwardly to their maximum extent by the application of the hydraulic elevating force on the body, the imposition of downweight on the drill pipe B and the mandrel 10 will shift the latter downwardly within the body 14-, to cause the lock and expander portion 38 to bear against the expander surface 30 and thereby mechanically force the cutter supporting members 23 and the cutters 27 outwardly to their maximum expanded position, the lock and expander portion 38 being disposed behind the lock portion 33 of the cutter supporting members. Thus, failure of the hydraulic pressure, after the cutters 27 have been expanded partially outward to form a partial formation shoulder B, will not prevent the cutters from being expanded outwardly to their maximum condition and locked in such maximum outwardly expanded position.

After the cutters 27 have been expanded outwardly, in the event the hydraulic pressure is relieved and the drill pipe B and mandrel 1i elevated, to elevate the cutters 27 above the formation shoulder E, the latter may drop back to their retracted position. However, before re lowering the drill pipe B and the apparatus A, the pumps need merely be started, to again hydraulically expand the cutters 27 outwardly to their maximum position, whereupon the apparatus can be lowered with pressure imposed in the cylinder space 22 to hold the cutters 27 in their outward expanded position, until the cutters again engage the formation shoulder E. Following such engagement, the mere imposition of the downwardly directed drilling weight on the drill pipe B and the tubular mandrel 10 will insure the retention of the cutters in their outwardly expanded position, even in the absence of the hydraulic pressure. However, since it is usual practice to continue pumping drilling fluid down through the drill pipe B and the apparatus A during the drilling operation, to flush the cuttings to the top of the well bore, the hydraulic force should always be avail-able to insure the retention of the cutters 27 in their expanded position.

The inventor claims:

1. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, and hydraulically movable means 011 said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel, to cause said expander means to expand said cutter means laterally outward.

2. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, said mandrel having a fluid passage communicating with the drill string, coengageable expander means on said mandrel and cutter means, hydraulically operable means on said body, and means for feeding fluid under pressure from said passage onto said hydraulically operable means to elevate said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

3. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward.

4. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel, to cause said expander means to expand said cutter means laterally outward, and coengaging means on said cutter means and mandrel for holding said cutter means laterally outward.

5. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward or" said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, said body having a cylinder portion above said expander means slidably and sealingly engaging said mandrel, said mandrel having a fluid passage communicating with the drill string and cylinder portion to feed fluid under pressure into said cylinder portion to elevate said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

6. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, said cutter means having a downward and inwardly inclined expander surface, said mandrel having an expander thereon slidable relatively along said surface to expand said cutter means laterally outward, said body having a cylinder portion above said expander slidably and sealingly engaging said mandrel, said mandrel having a fluid passage communicating with the drill string and cylinder portion to feed fluid under pressure into said cylinder portion to elevate said body and cutter means with respect to said mandrel to cause said expander to slide relatively along said expander surface and expand said cutter means laterally outward.

7. A rotary Well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, said cutter means having a downward and inwardly inclined expander surface, said mandrel having an expander thereon slidable relatively along said surface to expand said cutter means laterally outward, said body having a cylinder portion above said expander slidably and sealingly engaging said mandrel, said mandrel having a fluid passage communicating with the drill string and cylinder portion to feed fluid under pressure into said cylinder portion to elevate said body and cutter means with respect to said mandrel to cause said expander to slide relatively along said expander surface and expand said cutter means laterally outward, said cutter means having a holding surface adjacent and below said expander surface engageable with said expander, after said cutter means have been expanded laterally outward, to prevent retraction of said cutter means.

8. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, said body and mandrel having companion cylinder and piston portions slidably and sealingly engaging each other to provide a cylinder space therebetween, said mandrel having a fluid passage communicating with the drill string and cylinder space to feed fluid under pressure into said cylinder space to elevate said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

9. A rotary drill bit, including a main body, cutter means mounted on said body for expansion laterally of said body, a mandrel connectible to a drill string and telescoped within said body, coengageable expander means on said mandrel and said cutter means, hydraulically movable means on said body subject to the pressure of fluid in the drilling string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward, and means providing a slidable splined connection between said mandrel and body below said hydraulically movable means to transmit drilling torque from said mandrel to said body.

10. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanidng and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel telescoped within said body, hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward, and means providing a slidable splined connection between said mandrel and body below said hydraulically movable means to transmit drilling torque from said mandrel to said body.

ll. A rotary drill bit, including a main body having a longitudinal slot, cutter means in said slot and pivotally carried by said body for expansion laterally of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

12. A rotary drill bit, including a main body having a longitudinal slot, cutter means in said slot and pivotally carried by said body for expansion laterally of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, and hydraulically movable means on said body subject to the pressure of fluid in the drilling string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward.

13. A rotary well drilling bit, including a mandrel connectible to a drill string, a main body slidable along the exterior of that portion of said mandrel which is connectible to the drill string, means providing a slidable splined connection between said mandrel and body for transmitting drilling torque from said mandrel to said body, coengageable expander means on said mandrel and cutter means, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

14. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and telescoped within said body, said body being slidable along the exterior of that portion of said body which is connectible to the drill string, hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward, and means providing a slidable splined connection between said mandrel and body to transmit drilling torque from said mandrel to said body.

15. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally of said body, said body extending below said cutter means, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, and hydraulically movable on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

16. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, said body extending below said cutter means, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cut er means lateraily outward.

17. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally of said body, a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutter means, guide means on said body for said mandrel disposed below said expander means, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward.

18. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, guide means on said body for said mandrel disposed below said expanding and holding means, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward.

19. A rotary well drilling bit, including a main body, cutter means pivotally mounted on said body for movement about a pivot axis that remains a fixed distance from the body axis, a mandrel connectible to a drill string slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, coengageable expander means on said mandrel and cutsaid cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body, and hydraulically movable means on said body subject to the pressure of fluid in the drill string for elevating said body and cutter means with respect to said mandrel to hold said cutter means laterally outward.

References Cited in the file of this patent UNITED STATES PATENTS 1,611,282 Samuelson Dec. 21, 1926 2,457,628 Baker Dec. 28, 1948 2,699,921 Garrison Jan. 18, 1955 FOREIGN PATENTS 378,227 France Aug. 3, 1907 

